1. Field of the Invention
The present invention relates generally to centrifugal sewage pumps and more specifically to solids handling and grinder type centrifugal sewage pumps with two impellers that produce a discharge head, which is nearly twice as high as a single impeller centrifugal sewage pump.
2. Discussion of the Prior Art
The prior art does teach multi-staging of impellers with a discharge head that increases incrimentally by the number of impellers. However, the prior art pumps do not allow for large and stringy solids to freely flow from one stage to another without causing restrictions and loss of flow. The reason for the restrictions and loss of flow is the complex passages contained in the prior art pumps. The large and stringy solids become clogged in the complex passages.
Further, positive displacement, progressive cavity pumps do provide impressive discharge head. However, the positive displacement, progressive cavity pumps have high related maintenance, due to the wear of the rotor and stator and the close tolerance that must be maintained to deliver a high discharge head. The rotors and stators wear rapidly and thereby reduce the original tight tolerances that are required to deliver a high discharge head. Grinder pumps require a high discharge head to function correctly in pressure sewage systems, which is their primary application.
Accordingly, there is a clearly felt need in the art for centrifugal sewage pumps with two impellers, which do not have restrictive, complex passages for solid materials in sewage liquid to become clogged; do not require high maintenance; and which provide a discharge head height that is nearly twice that of a single impeller centrifugal pump, while drawing nearly the same amount of electrical power as a single impeller pump.